This invention relates to hypodermic needles.
The invention is particularly applicable to hypodermic needles for use with syringes for delivering intravenous fluids such as X-ray contrast fluids, drugs, blood products, and other fluids in situations where high flow rates are required or where the viscosity of the fluid to be injected is high. In a general context, the hypodermic needle of the invention is applicable for administering fluids via veins, arteries, intramuscular injections, intrathecal injections, and in other situations where the use of high flow or a fine needle would be an advantage The hypodermic needle of the invention is thus applicable in medical, dental, pharmaceutical and in veterinary practises.
The hypodermic needle of the invention may also have applications in other areas, for example in the chemical, petrochemical and engineering industries.
The streamline flow of fluid in a tube is defined by Pouseuille's formula as: ##EQU1## where: P.sub.2 -P.sub.1 is the pressure difference between the ends of the tube
r is the internal radius of the tube PA1 .mu. is the viscosity of the fluid PA1 l is the length of the tube
In order therefore to increase the flow in the tube, the possibilities are:
(i) to increase the pressure difference; PA0 (ii) to increase the radius of the tube; PA0 (iii) to decrease the length of the tube; PA0 (iv) to decrease the viscosity of the fluid.
The injection of viscous fluids in the medical field has posed problems for many years, since the length and the diameter of the needle are fixed by practical considerations. For example, in order to minimize discomfort to the patient and to be able to gain access to small veins, it is desirable to use needles with as small an external diameter as possible. There is a practical limit to the minimum length that a needle needs to be in order to gain access to deep veins. The viscosity of the fluid to be injected often cannot be changed. Thus the only parameter which can conveniently be varied, in order to increase the flow of the fluid, is the pressure.
To this end, mechanical injectors and levers have been used in order to increase the pressure, but the pressure still has to be limited by safety considerations when injecting into patients.